The present invention relates to an electronic musical instrument, and more particularly, to an electronic musical instrument wherein a digital representation of a waveshape is generated and this digital representation is processed through digital circuits.
In recent years, the technology of digital circuits has progressed remarkably, resulting in the development of various digital technics for generating musical tones. For one example, in U.S. Pat. No. 3,515,792, there is disclosed an electronic musical instrument in which a waveshape is stored in the form of digital representations and is repetitiously read out at a selectable rate thereby producing a musical note.
But this method for producing a musical note has disadvantages in that the quality of the produced musical tone is fixed by the waveshape which is previously stored, and that, for different tone qualities, different memories must be provided for storing different waveshapes.
For another example, in U.S. Pat. No. 3,809,786, there is disclosed a musical instrument wherein a desired waveshape is synthesized by adding the fundamental frequency component and the harmonic components. But this method of synthesizing a tone waveshape has a disadvantage in that the circuit is complicated because each frequency component must be processed independently of the other frequency components.
On the other side, in heretofore known analog type electronic musical instruments, analog filters are used to produce desired tone qualities. And an important disadvantage of an analog filter is that the filter character can not be changed unless one or more of the component parts of the filter is changed. Although techniques for designing conventional digital filters are well known, it is not economical to replace the analog filters in the heretofore known analog type electronic musical instrument by the corresponding conventional digital filters designed by the heretofore known design techniques, because these conventional digital filters have complicated circuits and are expensive.